In a recently published study on the initial rate of Na ion entering isolated frog skin from the epidermal side (J. Theor. Biol. 65, 653, 1977). We have given a detailed kinetic picture of the well known and important laboratory data published by Biber and by Cereijido and their co-workers. In this theoretical analysis we used a reasonable, multicompartment Na ion flow model to which the Continuous System Modeling Program (CSMP) was applied. In the coming year we intend to work mainly on two related projects. First, we plan to measure the initial rate of uptake of Na ion entering from the corium side of stripped epidermis, and also entering the corium itself when using whole skin. In this, the work of Biber and of Cereijido will serve as general guidelines. Secondly, we plan to simulate this Na ion uptake process in the same manner as we have done for Na ion uptake from the epidermal side of the skin (see above reference). A comparison of results of the two modes of Na ion uptake, we believe, should provide for interesting information on the role of the several Na ion pools in the epidermis in determining the characteristic flux patterns in the epithelial tissue.